The gas meter commonly used in the family is so-called "diaphragm gas meter" which comprises a measuring chamber, a valve element control chamber and a gas flow calculation and output device.
In the diaphragm gas meter, the measuring chamber may be divided into 4 measuring divisions. They are: inner-front division, inner-rear division, outer-front division and outer-rear division. Between the inner divisions and the outer divisions there is provided a moveable diaphragm. Two valves are provided at the entrance and the exit of the measuring chamber separately. By controlling the operation of the valves, gas may enter into the measuring chamber from the entrance and leave the chamber from the exit for further application. Measurement of the gas flow is based on the frequency of movement of the diaphragm. When the diaphragm moves, the position of a level which connects the diaphragm and the valve will change accordingly. As a result, the position of the valve will also change accordingly and the direction of gas flow will be changed. This change causes the diaphragm to move into the other direction. Under the above-said operation, a back-and-forth movement of the diaphragm will take place and the frequency of such back-and-forth movement is sensed, recorded and used to calculate the gas flow rate.
While the safety requirement and the automatic meter reading functions of the gas meter have become more and more important to users of gas meters, microcomputer-controlled gas meters have been developed and supplied to many users. In the microcomputer controlled gas meter, a safety control and communication module is provided about the valve element control chamber.
The measurement of gas flow in the microcomputer controlled gas meter is conducted by a microcomputer controller chip. A position detector is used to convert the frequency of movement of the diaphragm into electronic signals. The signals are then output to the microcomputer controller and the flow rate and the accumulated flow amount are calculated. The microcomputer controller may further provide functions such as safety control. Such safety control may be supported by a pressure sensor and an earthquake sensing element, both provided in the gas meter. The signals of gas pressure and earthquake sensing are transmitted into the microcomputer controller. When abnormal gas pressure or strong earthquake is sensed, the microcomputer controller ignites a shut-down valve to shut down the gas supplied to the gas meter, so to avoid any gas accident. The consumed amount of the gas flow and other safety monitoring information of gas supply may also be provided to a control center through a communication interface, such that reading and safety control of the gas meter may be conducted from a control center.
Due to its convenience, the microcomputer controlled gas meter has been well accepted by many families. However, for those users who has been already installed with conventional gas meters, it is necessary to replace these gas meters with microcomputer controlled gas meters. In order to save replacing costs, some additional modules and adapters have been disclosed. These adapters are so designed that conventional gas meters may be easily upgraded into microcomputer controlled gas meters, without the need of replacing the total gas meter.
U.S. Pat. No. 4,848,148 (assigned issued to American Meter Company) related to a method for the measurement of gas flow rate by counting the back-and-forth movement of the diaphragm inside the gas meter wherein the movement of the diaphragm is sensed by a sensing element. In this invention, the sensing element is a Hall IC device which can sense the movement of the diaphragm. The advantage of this invention rests in that the sensing element of this invention can be attached to the outer cover of the measuring chamber without changing the mechanical structure of the gas meter.
U.S. Pat. No. 5,369,598 (issued to Matsushita Electric Industrial Co., Ltd.) disclosed a method for the conversion of velocity and signals and the safety control of the gas flow rate. In this invention, a round turntable was provided inside the gas meter. The turntable rotates along with the gas flow and the magnets around the turntable passes a magnetic sensing device in sequence. The flow rate of the gas flow is thus calculated by counting the magnets passing the magnetic sensing device within a time unit. The major disadvantage of this invention is that an additional turntable shall be added into the gas meter and change the structure.
As to the modules of the computerized gas meter, several improvements were disclosed:
1. Earthquake Sensing Module
U.S. Pat. No. 5,408,457 (assigned to Osaka Gas Co., Ltd. and Kansai Gas Meter Co., Ltd.) disclosed an earthquake sensor for use inside a gas meter. The earth quake sensor is capable to sense strong earthquakes and comprises a steel ball hung inside a space surrounded by a continuous wall. When an earthquake takes place, the movement of the steel ball will cause a series of ON and OFF signals generated by an switch circuit located about the steel ball. This ON/OFF signals pattern may be used to determine the existence of an earthquake. The advantage of this design is that such earthquake sensor is simple and consumes very little electric power. Its disadvantage, on the other hand, is that it is not capable to measure the magnitude of an earthquake correctly. As a result, it is necessary to provide an additional logic circuit to determine whether a warning signal should be generated.
Japan Patent Publication No. 07-02048 disclosed an earthquake magnitude determination logic applicable to said U.S. Pat. No. 5,408,457. The determination logic of this patent includes a logic look up table wherein values of features of an earthquake such as total period of earthquake, number of cycles of shakes and time of shaking cycles are taking as factors. The advantage of this patent is that the look up table may be used to design the control circuit. Its disadvantage, however, is that the truth table is not applicable to areas where patterns of earthquake are different.
In addition to the above, in Douglas P. Ardunini's article "Smart Sensor Requirements for Second Generation Seismic Gas Shut-Off Valves" and in John Andrew Miche's U.S. Pat. No. 5,742,235, some features of earthquake were disclosed. According to their analysis, in an earthquake, its vertical waves (p-waves) will have a higher transmission speed than that of the horizontal waves (s-waves). On the other hand, the magnitude and the destroying power of the vertical wave are far smaller than that of the horizontal waves. As a result, in said U.S. Pat. No. 5,742,235, a micro vibration switch made from a semiconductor manufacture process was invented to sense the vertical waves of an earthquake. The advantage of this invention is that the structure of this earthquake sensor is simple and that its manufacture cost is relatively low. However, according to another analysis of the features of earthquakes, the magnitude of the vertical waves of an earthquake is very tiny (about 0.01 g). Under such a tiny scale, errors in the determination of an earthquake are easily caused, if only the vertical waves are sensed and are used as the only basis of the determination.
2. Pressure Sensing Module
In the computerized gas meter, its pressure sensor comprises a pressure switch using a diaphragm. The measuring area of gas pressure locates inside the valve element control chamber. Measurement of the gas pressure is conducted at the entrance of the gas meter. The advantage of this patent is the pressure switch consumes no electric power while it stands by. Its disadvantage, on the other hand, is that the diaphragm pressure switch has a certain volume. When it is inserted to the gas meter, it is necessary to modify the mechanical structure of the gas meter. Another problem is that the hysteresis phenomenon of the diaphragm pressure switch is obvious than that of general pressure gauges.
3. Gas Flow Shut-Down Mechanism
The most important feature of a microcomputer controlled gas meter is that it has a gas flow shut down mechanism. U.S. Pat. No. 5,408,457 (assigned to BLP Components Limited) disclosed an electric-magnetic valve to be used inside the gas meter. In this patent, a keep type solenoid is provided to push a valve so to shut down the gas flow. The advantage of this patent is that the control circuit is easy to design and that the gas flow may be shut down effectively. Its disadvantage is that, while the electric-magnetic valve is used, it is necessary to keep the balance between the volume of the valve seat and the resistance of the gas flow. Such requirement will make the design of the device difficult. In addition, if the shut-sown device shall be positioned inside the gas meter, due to the design of the valve seat, it is necessary to change the mechanical structure of the gas meter in a great scale.
4. Adapter
the adapter is a necessary device that enables the microcomputer control module to be adapted to a conventional gas meter so to upgrade the gas meter into a microcomputer controlled gas meter. Japanese patent NO. 8210893 (issued to Kokyo Gas Co., Ltd. And Kimmon Mfg Co., Ltd.) disclosed an adapter for the microcomputer controlled gas meter. In this patent the microcomputer control module was adapted to the conventional gas meter at the latter's front side, not on its top side. This design enables the computerized gas meter to reduce its height. However, similar to some of the above-mentioned prior art, while a pressure sensor and a shut-down valve shall be installed inside the gas meter, it is necessary to change the mechanical structure of the gas meter as well.